Thin film and method for manufacturing same

ABSTRACT

A totally new method for manufacturing a thin film wherein only an arbitrary small region is structurally controlled. The structure of a film is controlled by applying a force to the entire film or an arbitrary region of the film using a part having a sharp tip during the film-forming process or after finishing the film formation. At this time, the temperature of the film is set at the glass transition point of the amorphous region or higher. An atomic force microscope can be used as an apparatus for realizing this manufacturing method.

TECHNICAL FIELD

The present invention relates to a thin film manufacturing method, inwhich a structure of a thin film is controlled, used to providefunctional parts and components used in fields in which high-density andhigh-integration are required, as in memories and small electronicdevices such as a portable phone. The invention also relates to a thinfilm manufactured by controlling a structure.

BACKGROUND ART

There has been increasing demand for high-density and high-integrationparticularly in the areas of small electronic devices, specifically inthe fields of memory including semiconductor memory and optical memory,and portable phone. In semiconductor memory, the processing size in thechip has been approaching the processing limit of a photolithographytechnique. Accordingly, instead of the photolithography technique, thereis a need for a new processing technique that is more precise and moreaccurate. Increased precision of the components of memory devicesinevitably requires a corresponding level of integration for theperipheral devices such as a driving unit or a read/write head, as wellas parts and components of these devices. With further advancementtoward more precision, it will be even more difficult to follow theconventional procedure in which a large-area functional sheet or blockis cut into individual pieces to be processed and mounted on parts.

As a replacement of these techniques, there has been proposed atechnique in which an arbitrary minute area of a large-area sheet orblock is processed to construct a new structure. The technique allows arequired function to be obtained only in a region where it is required.The present invention relates to such a technique whereby a structurerequired for high-density and high-integration is formed in a controlledmanner for a required function in an arbitrary minute position of a verythin film.

In recent years, many types of functional thin films have been developedusing inorganic and organic materials, and many of these films have beenput to actual application. Examples of organic materials used for thispurpose include: polymer or low-molecular-weight films having opticalanisotropy; liquid crystal polymer films, liquid crystal oligomer films,or composite films of a low-molecular-weight liquid crystal and apolymer having dielectric or optical anisotropy; and ferroelectricpolymer films. As inorganic materials, conductive or ferroelectric metaloxide thin films have been developed. In organic materials, many ofthese functional thin films are produced by a method known as a wetdeposition method, in which a solution is spread over a substrate usingan applicator such as a spinner, bar coater, or slit die, and thesolvent is evaporated. A dry deposition method in which a thin film isdirectly vapor-deposited or sputtered on a substrate is also used. Forinorganic materials, a sol-gel method is widely used, in addition to thevapor deposition method. Generally, the thin film becomes functional orits function is improved when the structure of the thin film iscontrolled during or after the deposition process.

In one common method of controlling a structure of the thin film, a filmis deposited on a substrate having a micro structure on its surface, andthe resulting film structure is epitaxially controlled. In anothermethod, a micro structure of the film is controlled by mechanicallyapplying a force on the film. The most common example of the firstmethod is the orientation process for low-molecular-weight liquidcrystal films. In this process, a liquid crystal film is formed on asubstrate having non-flat structures of, for example, micro grooves onits surface, so that the liquid crystal molecules are oriented along thegroove structure. A well-known process of the second method isstretching applied to polymer films. In this technique, a polymer filmis stretched about two to five times the original by mechanicallyapplying a force in a single direction or two different directions ofthe film, so as to align the molecular chains along the directions ofapplied force. With aligning the directions of molecular chains by thestretching process, crystallinity of the film is improved. Further, thecrystal size becomes bigger, and orientation of crystals in the film canbe aligned by this process.

By controlling directions of molecules or microcrystals in the filmusing the foregoing methods, the following functions can be rendered.First, when molecules anisotropic with respect to refractive index areoriented along one direction, a film with refractive index anisotropycan be obtained. Further, by orienting the molecules along preciselycontrolled directions at each position of the film, an optical phaseshift film can be obtained that can precisely control a wavefront oflight. Such an optical phase shift film is necessary in the field ofdisplay to provide a phase shift filter for expanding the viewing angle.Further, the optical phase shift film is highly useful as a filter usedfor optical communications or optical processing unit.

Mechanical properties of the film can also be controlled by controllinga structure of the film. For example, when molecular chains of a polymerare oriented along one direction, the elastic modulus along thedirection of molecular chains becomes larger than that along a directionperpendicular to it. Thus, by aligning the molecular chains by a processlike the stretching process, a film with anisotropy in elastic moduluscan be obtained. If the film is anistropic with respect to elasticmodulus, then the film is also anisotropic with respect to soundvelocity. These properties of the film can be utilized to providevarious types of functional bodies or surface wave filters.

As described above, controlling a film structure is highly useful in awide variety of applications. However, all of the foregoing methods arefor controlling a structure of bulk materials. For example, thestretching process currently available for a polymer film can only beapplied to a film of a thickness exceeding 1000 nm, because the processis strongly influenced by the evenness of film thickness and tensility.Therefore films are broken easily in a case of thin film. As for thestructure control using an electric field or magnetic field, while theconventional methods allow a structure of a thin film to be controlledevenly over the film surface, it is difficult to control structures onlyin minute regions at arbitrary positions within the film plane. Further,in the orientation process for low-molecular-weight liquid crystal,non-flat structures are generally formed evenly over a wide area of thesubstrate. In some techniques of the orientation process,photolithography is used for forming different non-flat patterns indifferent regions on the substrate surface. However, so long asphotolithography is used, it is difficult to carry out the orientationprocess for a region of 1 μm² or smaller.

DISCLOSURE OF INVENTION

An object of the present invention is to overcome the foregoinglimitations of conventional techniques with use of a part having a sharptip, and thereby provide a novel method of manufacturing a thin filmwhereby a structure only in an arbitrary small region of the film iscontrolled.

To this end, the present invention provides a novel micro fabricationtechnique invented in view of the foregoing technical background.

Specifically, the invention provides:

(1) A method for manufacturing a thin film, comprising the step ofapplying a force, with a part having a sharp tip, onto an entire area orarbitrary region of a film during or after formation of the film, so asto control a structure of the film.

(2) A method for manufacturing a thin film, comprising the step ofapplying a force, with a part having a sharp tip, onto an entire area orarbitrary region of a film during or after formation of the film, with atemperature of the film maintained at or above a glass transitiontemperature of a amorphous region, so as to control a structure of thefilm.

(3) A method as set forth in (1) or (2), wherein the force applied onthe film derives from only the part having a sharp tip.

(4) A method as set forth in (1) or (2), wherein the force applied onthe film derives from the part having a sharp tip, and at least one ofan electric force generated by application of an electric field and amagnetic force generated by application of a magnetic field.

(5) A method as set forth in any one of (1) through (4), wherein thethin film is formed on a substrate.

(6) A method as set forth in any one of (1) through (5), wherein thepart having a sharp tip is a probe of an atomic force microscope.

(7) A method as set forth in any one of (1) through (6), wherein pluralareas of the film are simultaneously processed with plural parts havingsharp tips.

(8) A method for manufacturing a multi-layered film, in which a methodof any one of (1) through (7) is carried out on all of or some of thelayers of the multi-layered film.

(9) A thin film having a structure controlled by an applied forceexerted on an entire area or arbitrary region of the film by a parthaving a sharp tip during or after formation of the film.

(10) The thin film as set forth in (9), wherein a crystalline structureof crystals constituting the film is controlled.

(11) A thin film as set forth in (9), wherein an orientation directionof crystals constituting the film is controlled.

(12) A thin film as set forth in (9), wherein an orientation directionof molecules in crystals is controlled.

(13) A thin film as set forth in (9), wherein the film includes crystalsaccording to any two of or three of (10),

(11), and (12).

(14) A thin film as set forth in (9), wherein the film includes at leasttwo regions of crystals controlled according to at least one of (10)through (12).

(15) A thin film as set forth in any one of (9) through (14), whereinthe film is formed on a substrate.

(16) A multi-layered film having a structure according to any one of (9)through (15) controlled by carrying out the method of any one of (1)through (8) on all of or some of the layers of the multi-layered film.

A technical aspect of the present invention will now be described inmore detail. For convenience of explanation, a technique of theinvention is described through the case where a common atomic forcemicroscope is used. As used herein, “a part having a sharp tip” refersto a probe of the atomic force microscope, as an example. The presentinvention, however, is not limited in any way by the followingdescription.

In scanning a surface of a thin film with an atomic force microscope, aprobe of the microscope applies force on the thin film in twodirections: perpendicular to the film plane, and along the scandirection of the probe. The magnitudes of these two components of forcevary depending on the type of atomic force microscope used and theoperating modes. The present invention provides a technique that usessuch a force for controlling a structure of the thin film. Specifically,with a probe of an atomic force microscope, a thin film is scanned at anappropriate speed along the film plane while applying an appropriatemagnitude of force perpendicular to the film surface, so that anappropriate magnitude of force is also applied along the direction ofscan. With these forces, the technique achieves ordered orientation ofmicrocrystals or molecules in the thin film, along the scan direction ofthe probe.

In orienting microcrystals or molecules using a probe of a common atomicforce microscope, the present invention can control a structure of athin film with a thickness of 1000 nm or less. Further, a structure ofthe thin film can be controlled in a small region of a unit area assmall as 1 nm². As for larger areas, a single scan of a probe can onlycover an area up to 10⁴ μm². However, an area larger than several mm²can be controlled by carrying out a number of scans, or multiple scansat one time using a plurality of probes. Further, in an area covered bya single scan, the distance between controlled regions or positions ofcontrolled regions can be determined with accuracy within 10 nm.Further, the present invention can control a film structure not only fora thin film with a thickness of 1000 nm of less but also for a thin filmexceeding 1000 nm, or even a thin film exceeding 10 μm. Further, theprocess according to the present invention is not just limited totwo-dimensional structures, but three-dimensional structures can also becontrolled according to a method described below. First, a single-layerthin film is formed on a substrate by a means to be described later.After a structure of the film is controlled by the technique of thepresent invention, another single-layer thin film is formed on the firstthin film and a structure of the second film is controlled with thetechnique of the present invention. By repeating this procedure,three-dimensional structures can be controlled as well. Note that, inthis case, the stacked thin films may be made of the same material ordifferent materials. Further, each thin film can have any thickness.

As described above, with the ordered orientation of molecules ormicrocrystals, it is possible to control the optical, dielectric, ormechanical properties of the thin film, and thereby render anisotropy tothese properties. Further, with the technique of the present invention,a plurality of small regions can be formed in a single thin film asdescribed above, and the optical, dielectric, or mechanical property inthese regions of the film can be independently controlled.

With an atomic force microscope, the technique enables molecules ormicrocrystals to be orderly oriented along a direction of scan in asmall region of an arbitrary size arbitrarily positioned in the thinfilm. A single thin film may include a plurality of small regions.Further, since the atomic force microscope can scan in any direction,the molecules or microcrystals in each small region can be independentlyoriented in desired directions. Thus, with the technique of the presentinvention, a plurality of small functional regions can be formed in asingle thin film, and properties of these regions can be independentlycontrolled. The technique of the present invention therefore enables asingle thin film to integrate a plurality of small regions havingdifferent optical, dielectric, or mechanical properties.

The technique of the present invention can control a structure of a thinfilm made of an organic material or inorganic material.

An example of inorganic materials suitable for the invention is metalthin film and ceramic thin film with metal or metal oxide. However, theinvention is not limited to these materials, and a thin film made ofother materials can be used as well.

In order to form a thin film made of an inorganic material, commondeposition methods can be used, including, for example, a dry depositionmethod in which a thin film is directly vapor-deposited or sputtered ona substrate. In the case of ceramic materials, a wet deposition methodsuch as a sol-gel method can be also used.

When non-crystalline materials are used, a resulting film is in aso-called amorphous state. In some crystalline materials, a resultingfilm is structured from a large number of microcrystals. In other cases,microcrystals are interspersed in a amorphous state. The technique ofthe present invention is applicable regardless of the state of the film.

As for organic materials, the thin film may be made of a polymer,oligomer, or low-molecular-weight material.

The technique of the present invention can be used to control structuresof various polymeric materials, examples of which include: thermoplasticpolymers such as polyethylene or polypropylene; polyolefin resins suchas 4-methylpentene-1 resin or polybutene-1 resin; polyvinyl alcohols; acopolymer of ethylene and vinyl alcohol; a copolymer of ethylene andvinyl acetate; polyacrylonitrile; polybutadiene; polyisoprene; polyamideresins; polyester resins such as polyethylene terephthalate orpolybutyleneterephthalate; fluorinated resins as represented bypolytetrafluoroethylene, polytrifluoroethylene (PTrFE),polyvinylidenefluoride (PVDF) or copolymers of polytrifluoroethylene andpolyvinylidenefluoride (P(VDF-TrFE)). All of these materials arerepresentative examples of crystalline thermoplastic resins. Examples ofnon-crystalline thermoplastic resins include: polyvinyl chloride;polyvinylidene chloride; polyacrylate; polymethacrylate; polycarbonate;and polystyrene.

The technique of the present invention can also be used to control astructure of a thermosetting polymer, examples of which include: aphenol resin; a urea resin; a melamine resin; an alkyd resin; an acrylicresin; an epoxy resin; and a silicon resin. When a thermosetting resinis used, a structure of the film is controlled before the deposited filmis cured. By subsequent heat curing, a polymer film with highly orderedmolecular orientation can be obtained.

The technique of the present invention can also be used to control astructure of a heat-resistant resin, examples of which include:polyimide resin or aromatic polyamide known as a aramid resin;polyphenylene ether; polyphenylene sulfide; polyarylate;poly-p-phenylene; poly-p-xylene; poly-p-phenylenevinylene; andpolyquinoline.

Examples of conductive polymers include: polypyrrole; polythiophene;polyaniline; polyarylenevinylene; polythienylenevinylene; polyacen;polyacetylene; polyphenylene diamine; polyaminophenol;polyvinylcarbazole; polymer viologen; polyion complex; a charge transfercomplex such as TTF-TCNQ; and derivatives of these compounds. Thepresent invention can also be used for controlling a structure of a thinfilm made of conductive polymer materials as exemplified above.

With a controlled structure, the conductive polymer material can be usedin a wide range of fields, such as an emission source of anelectroluminescence element (EL); a counter conductive film for a touchpanel; various parts of displays including a liquid crystal display(LCD), plasma display panel (PDP), field emission display (FED), touchpanel, electrochromic element, and cathode-ray tube (CRT); and recordingmedia such as optic recording media, magneto-optic recording media,phase change recording media and magnetic recording media. The presentinvention is therefore highly useful in many industrial applications.

The foregoing materials are just some of representative examples ofthermoplastic resins, thermosetting resins, heat-resistant resins, andconductive organic polymers. As such, the invention is not just limitedto these examples and is applicable to various other polymer materials.

Further, the technique of the present invention is also applicable to athin film made of a liquid crystal material, such as polymer liquidcrystal, oligomer liquid crystal, and low-molecular-weight liquidcrystal. The liquid crystal material may be thermotropic or lyotropic.As a thermotropic liquid crystal, any of nematic liquid crystal, smecticliquid crystal, and cholesteric liquid crystal can be used. Further, inthe case of polymer liquid crystal or oligomer liquid crystal, thetechnique of the present invention is applicable to either of two typesof these liquid crystals: a backbone-type in which a rigid aromaticcyclic mesogen group is attached to the backbone; and a side chain-typein which the mesogen group is attached to the side chains. When a thinfilm of backbone-type liquid crystal is used in particular, a highlyanisotropic film can be obtained with respect to rigidity or otherphysical properties of the liquid crystal along the backbone directionand side chain direction. This enables micro functional elements such asa nanoactuator to be formed in the thin film.

As noted above, a method of forming an organic thin film is notparticularly limited. For example, a solution dissolving an organic filmmaterial may be spread over a substrate with the use of an applicatorsuch as a spinner, bar coater, or slit die, followed by evaporation ofthe solvent. Alternatively, a wet deposition method such as spraycoating or dipping may be used. Further, the organic material may bedirectly deposited on a substrate by a dry deposition method such assputtering, CVD, or PVD. Optionally, the film may be etched orpatterned, or a thin film of a different material may be stacked on thefilm.

When non-crystalline materials are used, a resulting film is in aso-called amorphous state. In some crystalline materials, a resultingfilm is structured from a large number of microcrystals. In other cases,microcrystals are interspersed in a amorphous state. The technique ofthe present invention is applicable regardless of the state of the film.

As described above, the present invention varies the micro-structure ofthe film by scanning a surface of a film with a probe of an atomic forcemicroscope, applying the force on the film in a direction of thicknessand a direction of scan. When non-crystalline materials are used, theforce orients the molecules along the scan direction of the probe. Onthe other hand, in the case of crystalline materials, three differentorientation types result. In the first type, the molecules are orientedalong the direction of scan, as in non-crystalline materials. In thiscase, the crystal structure of new crystals formed by re-orientation ofthe molecules remains the same, and only their direction is changed. Thesecond orientation type results when the film is polycrystalline. Inthis case, the scan made by the atomic force microscope rotates eachcrystal so that the crystals are aligned along the scan directionwithout changing the molecular chains in the crystals. As in the firsttype, the crystal structure does not change. In the case ofpolycrystals, a preferable orientation type is determined by thecondition which allows for more mobility between molecules in thecrystals and microcrystals. When the energy required to move thecrystals is lower than that required to move the molecules in thecrystals, each microcrystal can be rotated and oriented along the scandirection even when the scan made by the probe of the atomic forcemicroscope is carried out at a low temperature. In this case, themolecules in the crystals can be re-oriented along the scan direction bycarrying out the scan at a higher temperature. By the re-orientation ofthe molecules, the crystals disappear after the scan. In the thirdorientation type, a scan made by the atomic force microscope orients themolecular chains in the crystals along the scan direction, with theresult that the crystal structure is changed after the scan.

In order to orient the molecules or microcrystals of the film along thescan direction by the force of the probe of the atomic force microscope,a sufficient energy is required to allow for movement of the moleculesor microcrystals. One effective means to assist the movement is toincrease the film temperature above room temperature. Whennon-crystalline materials are used, it is effective to heat the film toa temperature at which the molecules start to undergo thermal motion,i.e., at or above the glass transition temperature (Tg). On the otherhand, in the case of crystalline materials, the microcrystals, as wellas the molecular chains, can be oriented along the scan direction. Inthis case, the scan made by the probe should avoid molecule movement inthe crystals. It is therefore preferable that the scan be carried out ata lower temperature than that for orienting the molecules. Specifically,the scan can be effectively carried out at a temperature no less thanglass transition temperature of a amorphous region betweenmicrocrystals, and at a temperature sufficiently below melting point(Tm) of the crystals. On the other hand, the molecules in thecrystalline regions can be effectively oriented by heating the film to atemperature in the vicinity of melting point of the crystals.

When the molecules forming the film contain polar groups such as anamino group, ammonium group, or hydroxyl group, or halogen elements suchas F or Cl, an electric field can be effectively applied to the film inorder to facilitate movement of the molecules or microcrystals by theprobe scan. For example, many low-molecular-weight liquid crystals areanisotropic with respect to dielectric constant along the short axis andthat along the long axis. It is therefore possible to assist alignmenteffectively by applying of an electric field. The effect of applying anelectric field is particularly notable in ferroelectric materials, inwhich the direction of spontaneous polarization in the film is reversedwhen an electric field at or greater than the coercive electric field(Ec) is applied.

For organic ferroelectric materials, it is particularly effective toapply an electric field during a probe scan. Examples of organicferroelectric materials include: vinylidenefluoride polymers (PVDF);vinylidenefluoride oligomers; vinylidenefluoride copolymers asrepresented by a random copolymer of vinylidenefluoride andpolytrifluoroethylene (P(VDF-TrFE)); odd-numbered nylon resins such asnylon 7, nylon 9, nylon 11, or nylon 13; and alternating copolymers ofvinylidenecyanide and vinyl acetate. In liquid crystal materials, theeffect of applying an electric field is particularly notable inferroelectric liquid crystals as represented by a cholesteric liquidcrystal having chiral C*. All of the organic ferroelectric liquidcrystals as exemplified above are order-disorder type ferroelectricmaterials. As for inorganic ferroelectric materials, it is highlyeffective to apply an electric field during a probe scan to theinorganic crystals of an order-disorder type ferroelectric material suchas potassium hydrogen phosphate, Rochelle salt, glycine sulfate, sodiumnitrate, or thiourea. In the case of inorganic displacement-typeferroelectric materials, it is effective to apply an electric field to aceramic ferroelectric including, for example, barium titanate crystals,zirconium titanate, and lead titanate. It is to be noted thatapplication of an electric field is effective not only for the foregoingferroelectric materials but also for all kinds of ferroelectricmaterials in general.

The application of an electric field is effective regardless of whetherthe applied field is a DC electric field or AC electric field. Theeffect can be obtained when the magnitude of the applied electric fieldis 0 V or greater, but an even greater effect can be obtained forferroelectric materials when an electric field equal to or greater thanthe coercive electric field (Ec) is applied. Likewise, in the case of anAC electric field, a greater effect can be obtained when the peak valueis equal to or greater than the coercive electric field (Ec). Anelectric field perpendicular to the film can be generated by applying avoltage across the probe of the atomic force microscope and a conductivesubstrate on which the film is formed. An electric field parallel to thefilm plane can be generated by applying a voltage across the probe andone or more independent electrodes formed on the film surface, or byapplying a voltage across two or more independent probes provided in theatomic force microscope. In these cases, the probe or probes of theatomic force microscope need to be conductive. Such a conductive probecan be obtained by depositing a highly conductive metal such as Au, Pt,Ag, or Rh on a surface of a silicon stylus having a sharp tip, or bydoping a silicon material of a stylus with a large amount of impuritiessuch as P.

Note that, the ferroelectric thin film can be used in speakers,microphones, ultrasonic transducers, pressure sensors, optical switches,capacitors, optical memory, ferroelectric memory, optical waveguides,surface wave filters, infrared detectors, and light modulating devices,for example. The performance of these devices can be improved by usingthe ferroelectric thin film whose structure is controlled by a method ofthe present invention.

When the molecules of the film have a magnetic dipole, it is effectiveto apply a magnetic filed to the film in order to facilitate movement ofthe molecules or microcrystals by the probe scan. Application of amagnetic field is particularly effective in ferromagnetic materials,because the direction of magnetization in ferromagnetic film is reversedby applying coercive magnetic field. One method to assist alignment byapplying a magnetic field to the film is using a magnetic probe.Specifically, this can be achieved with a probe whose tip has beencoated by sputtering with a magnetic metal such as Fe, Ni, or Co, or acompound containing these metals and magnetized by applying magneticfield. With this method, the film experiences the magnetic field at alltimes. Alternatively, the tip of the probe and a nearby region of thefilm may be magnetized by flowing a current through a magnetic coilprovided in the vicinity of the probe tip. In this case, the magneticfield can be turned ON or OFF depending on purpose.

In organic materials, the n electrons of the benzene ring easily form amagnetic dipole. Therefore, for rigid molecules containing a largenumber of benzene rings, it is effective to apply a magnetic fieldduring a probe scan. This is particularly effective for heat-resistantpolymers as exemplified above, namely, aromatic polyamide, polyphenyleneether, polyphenylene sulfide, polyarylate, poly-p-phenylene,poly-p-xylene, poly-p-phenylenevinylene, and polyquinoline, which aresome of the examples of rigid molecules containing a large number ofbenzene rings. As for liquid crystal materials, many of them containaromatic rings, which render rigidity to the structure. Therefore,application of a magnetic field is effective for both polymer liquidcrystals and low-molecular-weight liquid crystals. Application of amagnetic field is also effective for inorganic magnetic materials,particularly ferromagnetic materials containing metals such as Fe, Ni,or Co, or their oxides or alloys of these metals. Further, in scanningthe ferromagnetic material, it is highly effective to apply a magneticfield equal to or greater than the coercive magnetic field, as in thecase of the ferroelectric material in which an electric field equal toor greater than the coercive electric field can be effectively applied.

A substrate used for supporting a thin film manufactured by a method ofthe present invention is not particularly limited. The material, shape,structure, size, and other properties of the substrate can be suitablyselected according to the intended use or required functions. Forexample, a functional substrate may be a transparent substrate,light-shielding substrate, a conductive substrate, semiconductivesubstrate, insulating substrate, or gas barrier substrate. Specificexamples of such functional substrates include: a glass substrate, aceramic substrate, an organic or inorganic semiconductor substrate, agraphite substrate, an organic conductive substrate, a metal substrate,and a resin film.

In using the atomic force microscope, the operation mode of scanning thefilm surface may be either a dynamic-mode in which the probe is not indirect contact with the film surface or is in contact with the filmsurface only intermittently, or a contact-mode in which the probe is incontact with the film surface at all times. Of these two operationmodes, the contact-mode allows the force to be applied perpendicular tothe film and along the scan direction, and therefore has more effect onthe film. In the dynamic-mode, the force perpendicularly applied on thefilm by the probe is intermittent, and the magnitude of force in thescan direction is small. The dynamic-mode or contact-mode needs to besuitably selected taking into consideration the toughness of thematerial used and the mobility of the molecules in the film. In the caseof organic materials, the contract-mode is generally more suitablebecause the polymer material generally has good toughness and restrictedmobility. The dynamic-mode is suitable for some low-molecular-weightmaterials.

In operating the probe in the contact-mode or dynamic-mode, the hardnessof the cantilever (a support for the probe) has a profound effect on theresulting orientation of the molecules or microcrystals constituting thefilm. The extent of damage on the film is also largely dependent on thehardness of the cantilever. When the film is made of a soft material, anexceptionally soft cantilever needs to be used to prevent damage on thefilm. Even for a polymer film, a soft cantilever is required when a scanis made at a high temperature in the vicinity of the melting point.Specifically, for organic materials, a cantilever with a spring constantof no greater than 40 N/m is preferable in the dynamic-mode, and acantilever with a spring constant of no greater than 4 N/m is preferablein the contact-mode. Further a cantilever with a spring constant of nogreater than 0.4 N/m is more preferable in the contact-mode. Forinorganic materials, the hardness of the cantilever is not sorestricted, but a cantilever with a spring constant of no greater than40 N/m can be preferably used.

When the film is made of polymer, scanning the film with a probecontrols the orientation of the molecular chains along the scandirection in the case of non-crystalline polymers. Generally, the filmtemperature during a scan should preferably be maintained at or abovethe glass transition temperature. However, the optimum film temperaturethat provides the most preferable orientation varies depending on thematerial of the film. Usually, the most preferable temperature isdetermined by the temperature characteristics concerning film toughnessand mobility of the molecules. Further, when the film is structured froma large number of microcrystals of a crystalline polymer, it isgenerally preferable to scan the film at a temperature range from thetemperature at or above the glass transition temperature of a amorphousregion of the film to the temperature sufficiently below the meltingpoint of the crystal region. However, as in the case of thenon-crystalline polymer, the optimum temperature that provides the mostpreferable orientation varies depending on the material of the film. Byscanning the film at the optimum temperature of the material used, themicrocrystals can be desirably oriented. In above case, however, it isoften difficult to orient the microcrystals using dynamic-mode. It istherefore more preferable to carry out the operation in thecontact-mode. Further, by scanning the film at a temperature in thevicinity of the melting point of the crystal region of the crystallinepolymer, the molecular chains can be oriented in the scan direction.

The foregoing described the technique of the present invention based onan example in which a part having a sharp tip is a probe of an atomicforce microscope. However, the device used in the present invention isnot just limited to the atomic force microscope, and the invention isapplicable to various other devices as exemplified below. For example,as a manufacturing device or processing device for a thin film accordingto the present invention, the invention can use any device as long as ithas a part having a sharp tip, and has a mechanism that enables thesharp tip to apply force on the film and scan the film along the filmplane. Such manufacturing devices or processing devices have basicstructures similar to that of the atomic force microscope, but do notnecessarily have the feedback function of the atomic force microscope.Further, the present invention can also use devices that additionallyinclude a mechanism for controlling the magnitude of force applied onthe film through the sharp tip. Further, the invention can also use adevice designed to include more than one part having a sharp tip andthereby allows the process to be quickly carried out over a large area.As for the horizontal scan, the scan can be made not only by moving theprobe but also by moving the thin film being processed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an atomic force micrograph of a thin film surface (area: 10μm×10 μm), prior to a scan for the orientation control by an atomicforce microscope, according to Example 1 of the present invention.

FIG. 2 is a schematic illustration of crystals and molecules on a thinfilm on graphite, before and after the film is scanned for theorientation control at a temperature of 50° C. or higher, according toExample 1 of the present invention.

FIG. 3 is an atomic force micrograph of a thin film surface on graphite(area: 2 μm×2 μm), before and after the film is scanned for theorientation control at a temperature of 80° C., according to Example 1of the present invention.

FIG. 4 is an atomic force micrograph of a thin film surface (area: 4μm×4 μm), before and after the thin film is scanned with an appliedvoltage, according to Example 2 of the present invention.

FIG. 5 is a schematic illustration of crystals and molecules on a thinfilm on graphite, before and after the film is scanned for theorientation control at 135° C. by using a probe of an atomic forcemicroscope, according to Example 3 of the present invention.

FIG. 6 is an atomic force micrograph of a thin film surface on graphite(area: 1 μm×1 μm), before and after the film is scanned for theorientation control at 135° C. by using a probe of an atomic forcemicroscope, according to Example 3 of the present invention.

FIG. 7 is an atomic force micrograph of a thin film surface (area: 1μm×1 μm) formed on a glass substrate, according to Example 4 of thepresent invention.

FIG. 8 is a schematic view illustration of crystals of the thin filmshown in FIG. 7.

FIG. 9 is a schematic illustrating how molecules are oriented along ascan direction by a scan using a probe on the thin films formed on aglass substrate, on a Pt layer, on an Au layer, or on an Al layer,according to Examples 4 through 7 of the present invention.

FIG. 10 is an atomic force micrograph of a thin film surface on glass(area: 2 μm×2 μm), before and after the film is scanned for orientationcontrol by using a probe of an atomic force microscope, according toExample 4 of the present invention.

FIG. 11 is an atomic force micrograph of a surface of a thin film formedon a Pt layer (area: 2 μm×2 μm), according to Example 5 of the presentinvention.

FIG. 12 is an atomic force micrograph of a thin film surface on Pt layer(area: 2 μm×2 μm), before and after the film is scanned for orientationcontrol, according to Example 5 of the present invention.

FIG. 13 is an atomic force micrograph of a surface of a thin film formedon an Al layer (area: 2 μm×2 μm), according to Example 6 of the presentinvention.

FIG. 14 is an atomic force micrograph of the thin film surface on Allayer (area: 2 μm×2 μm), before and after the thin film formed on the Allayer is scanned, according to Example 6 of the present invention.

FIG. 15 is an atomic force micrograph of a surface of a thin film formedon an Au layer (area: 2 μm×2 μm), according to Example 7 of the presentinvention.

FIG. 16 is an atomic force micrograph of the thin film surface on Aulayer (area: 2 μm×2 μm), before and after the film is scanned fororientation control, according to Example 7 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A specific embodiment and effects of the present invention will bedescribed below by way of Examples. It should be understood, however,that the invention is not limited in any way by the materials, devices,or experimental conditions used in the following Examples, but on thecontrary, the invention is to cover all modifications, equivalents, andalternatives falling within the scope of the invention as defined in thespecification and appended claims.

In Example 1, 30 mg of a random copolymer of vinylidenefluoride andtrifluoroethylene (P(VDF-TrFE)) (VDF/TrFE ratio: 68 to 80/32 to 20),which is ferroelectric polymer, was dissolved in 10 ml ofmethylethylketone (MEK), so as to prepare a P(VDF-TrFE) solution. Thesolution was spin-coated on a graphite substrate used as a conductivesubstrate. The resulting thin film was then subjected to a heattreatment for one hour at 140° C., so as to obtain a ferroelectriclamellar microcrystalline thin film of 25 nm thick. The film had a glasstransition temperature of −25° C., and a melting point in the vicinityof 150° C. The lamellar microcrystals had c axes (molecular chain axes)isotropically oriented in the film plane. FIG. 1 depicts surfacetopography of the film observed with an atomic force microscope.

A surface of the film heated at 50° C. or higher was scanned incontact-mode using the atomic force microscope. As a result, thelengthwise direction of the lamellar microcrystals oriented along thedirection of the scan. FIG. 2 schematizes how the crystals are orientedby the scan for orientation control using a probe of atomic forcemicroscope.

The regularity of orientation was improved by the scan with a rise inthe film temperature, whereas a higher film temperature caused moredamage on the film surface during a scan. The extent of damage on thefilm surface caused by the probe scan varied depending on the springconstant of the cantilever. By using such parameters as filmtemperature, spring constant of the cantilever, and probe pressure,orientation of lamellar crystals was studied extensively. It was foundas a result that the lamellar crystals was oriented when the film wasscanned with a probe at the film temperature of 80° C., which is higherthan 50° C., using a soft silicon cantilever having a spring constant of0.2 N/m. FIG. 3 depicts an atomic force micrograph of the film surfacescanned for the orientation control under these conditions (observed at30° C.). In FIG. 3, the lower half shows an image after the scan for theorientation control. As clearly indicated in FIG. 3, the lamellarcrystals are desirably oriented along the scan direction. By thussuitably setting the spring constant of the cantilever and the filmtemperature, microcrystals were oriented along the scan direction of theprobe using an atomic force microscope.

In Example 2, 50 mg of a random copolymer of vinylidenefluoride andtrifluoroethylene (P(VDF-TrFE)) (VDF/TrFE ratio: 68 to 80/32 to 20) usedin Example 1 was dissolved in 10 ml of methylethylketone (MEK), so as toprepare a P(VDF-TrFE) solution. As in Example 1, the solution wasspin-coated on a graphite substrate. The resulting thin film was thensubjected to a heat treatment for one hour at 140° C., so as to obtain aferroelectric lamellar microcrystalline thin film of 75 nm thick. Thefilm was heated at 80° C., and was scanned for the orientation controlin contact-mode using an atomic force microscope with an applied voltageof 7 V, which is equal to or higher than the coercive electric field ofthe film, across the cantilever and the conductive substrate bearing thefilm. Here, the scan for the orientation control was made with aconductive cantilever, which additionally had a metal coating on thecantilever used in Example 1 (silicon cantilever with a spring constantof 0.2 N/m). FIG. 4 depicts the result obtained by the scan in thepresence of an electric field. In FIG. 4, the central portioncorresponds to a region scanned for the orientation control in thepresence of an electric field. It can be seen that the lamellar crystalsare more desirably oriented in this region along the scan direction, ascompared with the result shown in FIG. 3 (Example 1). In ferroelectricpolymers, the improved orientation obtained in the presence of anelectric field can be attributed to helical deformation of the C-Cbackbone caused by the rotation of a H-F permanent dipole around the C-Cbackbone, and the corresponding slight deformation of the crystals,which affords more crystal mobility.

In Example 3, a surface of the p(VDF-TrFE) film (thickness of 75 nm)used in Example 2 was scanned for the orientation control at 135° C.,which is higher than 80° C., using the cantilever used in Example 1.Here, the scan was made in the absence of a voltage across the probe andsubstrate. As a result, the lamellar crystals aligned with thelengthwise direction perpendicular to the scan direction, appeared asshown in FIG. 5. This is the result of increased mobility of themolecular chains afforded by the increased temperature much higher thansuitable temperature 80° C., used in Example 1, for the orientationcontrol of the P(VDF-TrFE) microcrystals. Thus, scanning the filmsurface at 135° C. with the probe of the atomic force microscopecontrols the molecular chains orientation, not the orientation oflamellar crystals, along the scan direction, thereby forming newlamellar crystals oriented perpendicular to the scan direction. FIG. 6depicts an atomic force micrograph of the film surface obtained by thescan for orientation control under these conditions.

In Example 4, a P(VDF-TrFE) thin film of 75 nm thick was formed on aglass substrate (MATSUNAMI MICRO COVER GLASS) according to the procedureof Example 1. FIG. 7 depicts an atomic force micrograph of the resultingfilm surface (observed at 30° C.). It can be seen from FIG. 7 that theP(VDF-TrFE) on the glass substrate is composed of lamellar crystalswhose lamellar planes are grown parallel to the in-plane direction ofthe substrate. FIG. 8 schematizes the P(VDF-TrFE) crystals shown in FIG.7. As clearly shown in FIG. 8, the P(VDF-TrFE) molecular chains in thecrystals formed on the glass substrate are oriented perpendicular to thesubstrate, as compared with Example 3 in which the P(VDF-TrFE) molecularchains in the crystals formed on the graphite substrate were orientedparallel to the in-plane direction of the substrate.

The thin film heated to 130° C. was scanned in the direction of arrowshown in FIG. 9, using the cantilever of Example 1. FIG. 10 depicts aresulting atomic force micrograph (observed at 30° C.). It can be seenfrom FIG. 10 that, in a region scanned at 130° C., lamellar crystalswhose lamellar plane are grown perpendicular to the substrate areformed. Further, as in Example 3, the crystals were oriented so thattheir long axes were perpendicular to the direction of the scan carriedout at 130° C. These results clearly indicate that the lamellar crystalswith the orientation perpendicular to the scan direction were formed asa result of a change in the orientation state of the molecular chains,from the perpendicular state with respect to the in-plane direction ofthe substrate to the orientation along the scan direction, caused by anapplied force exerted on the molecular chains at 130° C. by the probescan, as schematically illustrated in FIG. 9. Thus, with the techniqueof the present invention, the molecular chains perpendicular to thesubstrate can be oriented along the in-plane direction of the substrateand the scan direction of the probe.

In Example 5, platinum (Pt) (50 nm thick) was sputtered on a Si wafer,so as to obtain a substrate coated with a Pt thin film. According to theprocedure of Example 4, a P(VDF-TrFE) thin film (75 nm thick) was formedon the substrate. FIG. 11 depicts an atomic force micrograph of theresulting thin film surface (observed at 30° C.). It can be seen fromFIG. 11 that the P(VDF-TrFE) on the Pt layer is composed of lamellarcrystals whose lamellar planes are grown parallel to the substrate, asin Example 4. The thin film heated at 135° C. was scanned for theorientation control in the direction of arrow shown in FIG. 9, using thecantilever of Example 1. FIG. 12 depicts the resulting atomic forcemicrograph (observed at 30° C.). As can be seen from FIG. 12, thelamellar crystals with the lengthwise orientation perpendicular to thescan direction were formed on the Pt layer as a result of a change inthe orientation state of the molecular chains, from the perpendicularstate with respect to the in-plane direction of the substrate to theorientation along the scan direction, caused by an applied force exertedon the molecular chains at 135° C. by the probe scan, as in Example 4.

In Example 6, aluminum (Al) (50 nm thick) was vapor-deposited on a Siwafer, so as to obtain a substrate coated with an Al thin film.According to the procedure of Example 4, a P(VDF-TrFE) thin film (75 nmthick) was formed on the substrate. FIG. 13 depicts an atomic forcemicrograph of the resulting thin film surface (observed at 30° C.). Itcan be seen from FIG. 13 that the P(VDF-TrFE) on the Al layer iscomposed of lamellar crystals whose lamellar planes are grown parallelto the plane of the substrate, as in Example 4. The thin film heated at130° C. was scanned for the orientation control in the direction ofarrow shown in FIG. 9, using the cantilever of Example 1. FIG. 14depicts the resulting atomic force micrograph (observed at 30° C.). Ascan be seen from FIG. 14, the lamellar crystals with the lengthwiseorientation perpendicular to the scan direction were formed on the Allayer as a result of a change in the orientation state of the molecularchains, from the perpendicular state with respect to the in-planedirection of the substrate to the orientation along the scan direction,caused by an applied force exerted on the molecular chains at 130° C. bythe probe scan, as in Example 4.

In Example 7, gold (Au) (50 nm thick) was vapor-deposited on a Si wafer,so as to form a substrate coated with a Au thin film. According to theprocedure of Example 4, a P(VDF-TrFE) thin film (75 nm thick) was formedon the substrate. FIG. 15 depicts an atomic force micrograph of theresulting thin film surface (observed at 30° C.). It can be seen fromFIG. 15 that the P(VDF-TrFE) on the Au layer is composed of lamellarcrystals whose lamellar planes are grown parallel to the plane of thesubstrate, as in Example 4. The thin film heated at 130° C. was scannedfor the orientation control in the direction of arrow shown in FIG. 9,using the cantilever of Example 1. FIG. 16 depicts the result obtainedwith the atomic force microscope (observed at 30° C.). As can be seenfrom FIG. 16, the lamellar crystals with the lengthwise orientationperpendicular to the scan direction were formed on the Au layer as aresult of a change in the orientation state of the molecular chains,from the perpendicular state with respect to the in-plane direction ofthe substrate to the orientation along the scan direction, caused by anapplied force exerted on the molecular chains at 130° C. by the probescan, as in Example 4.

As can be seen from the results of the foregoing Examples, a methodaccording to the present invention enables the molecules to be orientedin a specific direction with respect to a scan direction of the probe,irrespective of the initial spatial orientation of the molecules. Thus,with the technique of the present invention, limitations of conventionaltechniques can be overcome, and the molecules or microcrystals in anysmall region of the thin film can be oriented in an arbitrary directionto control the structure in the small region. As a result, variousproperties of the small region can be controlled, including optical,electrical, and mechanical properties such as refractive index,dielectric constant, and elastic modulus, respectively.

INDUSTRIAL APPLICABILITY

The present invention can be used for controlling refractive index of athin film in the fields of optical communications filter, display, andoptical memory, for example. The invention is also useful in formationof various micro parts when mechanical constants such as elastic modulusare controlled. Further, by controlling a sound velocity, the inventionis applicable to surface wave filters. When used for controlling adielectric constant, the invention is applicable to micro circuit boardswhich incorporate various elements such as a capacitor. As set forthabove, the present invention covers a wide range of field, includingoptical communications, electronic devices, and common machinery. Whenused in these and other fields, the invention can realize high-qualityparts and devices unattainable by conventional techniques.

1. A method for manufacturing a thin film, comprising the step ofapplying a force, with a part having a sharp tip, onto an entire area orarbitrary region of a film during or after formation of the film, so asto control a structure of the film.
 2. A method for manufacturing a thinfilm, comprising the step of applying a force, with a part having asharp tip, onto an entire area or arbitrary region of a film during orafter formation of the film, with a temperature of the film maintainedat or above a glass transition temperature of a amorphous region, so asto control a structure of the film.
 3. A method as set forth in claim 1,wherein the force applied on the film derives from only the part havinga sharp tip.
 4. A method as set forth in claim 2, wherein the forceapplied on the film derives from only the part having a sharp tip.
 5. Amethod as set forth in claim 1, wherein the force applied on the filmderives from the part having a sharp tip, and at least one of anelectric force generated by application of an electric field and amagnetic force generated by application of a magnetic field.
 6. A methodas set forth in claim 2, wherein the force applied on the film derivesfrom the part having a sharp tip, and at least one of an electric forcegenerated by application of an electric field and a magnetic forcegenerated by application of a magnetic field.
 7. A method as set forthin claim 1, wherein the thin film is formed on a substrate.
 8. A methodas set forth in claim 2, wherein the thin film is formed on a substrate.9. A method as set forth in claim 1, wherein the part having a sharp tipis an atomic force microscope.
 10. A method as set forth in claim 2,wherein the part having a sharp tip is an atomic force microscope.
 11. Amethod as set forth in claim 1, wherein plural areas of the film aresimultaneously processed with plural parts having sharp tips.
 12. Amethod as set forth in claim 2, wherein plural areas of the film aresimultaneously processed with plural parts having sharp tips.
 13. Amethod as set forth in claim 1, wherein the structure of the film iscontrolled by controlling (i) a crystalline structure of crystalsconstituting the film, (ii) an orientation direction of crystalsconstituting the film, (iii) an orientation direction of molecules inthe crystals, or (iv) any combination of (i) through (iii).
 14. A methodas set forth in claim 2, wherein the structure of the film is controlledby controlling (i) a crystalline structure of crystals constituting thefilm, (ii) an orientation direction of crystals constituting the film,(iii) an orientation direction of molecules in the crystals, or (iv) anycombination of (i) through (iii).
 15. A method as set forth in claim 1,wherein the structure of the film is controlled by scanning a filmsurface with the part having a sharp tip.
 16. A method as set forth inclaim 2, wherein the structure of the film is controlled by scanning afilm surface with the part having a sharp tip.
 17. A method as set forthin claim 1, wherein the film is made of an organic polymer material. 18.A method as set forth in claim 2, wherein the structure of the film iscontrolled by scanning a film surface with the part having a sharp tip.19. A method as set forth in claim 1, wherein the structure of the filmis controlled by scanning a film surface with the part having a sharptip, and wherein the structure of the film is controlled by controlling(i) a crystalline structure of crystals constituting the film, (ii) anorientation direction of crystals constituting the film, (iii) anorientation direction of molecules in the crystals, or (iv) anycombination of (i) through (iii).
 20. A method as set forth in claim 2,wherein the structure of the film is controlled by scanning a filmsurface with the part having a sharp tip, and wherein the structure ofthe film is controlled by controlling (i) a crystalline structure ofcrystals constituting the film, (ii) an orientation direction ofcrystals constituting the film, (iii) an orientation direction ofmolecules in the crystals, or (iv) any combination of (i) through (iii).21. A method for manufacturing a multi-layered film, in which a methodof claim 1 is carried out on all of or some of the layers of themulti-layered film.
 22. A thin film having a structure controlled by aforce applied on an entire area or arbitrary region of the film by apart having a sharp tip during or after formation of the film.
 23. Athin film as set forth in claim 22, wherein a crystalline structure ofcrystals constituting the film is controlled.
 24. A thin film as setforth in claim 22, wherein an orientation direction of crystalsconstituting the film is controlled.
 25. A thin film as set forth inclaim 22, wherein an orientation direction of molecules in crystals iscontrolled.
 26. A thin film as set forth in claim 22, wherein the filmincludes crystals wherein at least two of a crystalline structure ofcrystals constituting the film is controlled, an orientation directionof crystals constituting the film is controlled and an orientationdirection of molecules in crystals is controlled.
 27. A thin film as setforth in claim 22, wherein at least two regions of crystals constitutingthe film are controlled according to at least one of a crystallinestructure of crystals constituting the film is controlled, anorientation direction of crystals constituting the film is controlledand an orientation direction of molecules in crystals is controlled. 28.A thin film as set forth in claim 22, wherein the film is made of anorganic polymer material.
 29. A thin film as set forth in claim 22,wherein the film is formed on a substrate.
 30. A multi-layered filmhaving a structure controlled by a force applied on an entire area orarbitrary region of the film by a part having a sharp tip during orafter formation of the film controlled by carrying out the method ofclaim 1 on all or some of the layers of the multi-layered film.
 31. Amulti-layered film having a structure controlled by a force applied onan entire area or arbitrary region of the film by a part having a sharptip during or after formation of the film controlled by carrying out themethod of claim 2 on all or some of the layers of the multi-layeredfilm.